diff mbox series

[06/10] LSM: Infrastructure management of the file security blob

Message ID 748e4bca-41f1-c43b-a691-bf6b3d910793@schaufler-ca.com (mailing list archive)
State Superseded
Headers show
Series LSM: Module stacking in support of S.A.R.A and Landlock | expand

Commit Message

Casey Schaufler Sept. 11, 2018, 4:42 p.m. UTC 
Move management of the file->f_security blob out of the
individual security modules and into the infrastructure.
The modules no longer allocate or free the data, instead
they tell the infrastructure how much space they require.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 include/linux/lsm_hooks.h  |  1 +
 security/apparmor/lsm.c    | 19 +++++++-------
 security/security.c        | 54 +++++++++++++++++++++++++++++++++++---
 security/selinux/hooks.c   | 25 ++----------------
 security/smack/smack.h     |  5 ++++
 security/smack/smack_lsm.c | 26 +++++++-----------
 6 files changed, 78 insertions(+), 52 deletions(-)

Comments

Kees Cook Sept. 13, 2018, midnight UTC | #1 
On Tue, Sep 11, 2018 at 9:42 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
> Move management of the file->f_security blob out of the
> individual security modules and into the infrastructure.
> The modules no longer allocate or free the data, instead
> they tell the infrastructure how much space they require.
>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>  include/linux/lsm_hooks.h  |  1 +
>  security/apparmor/lsm.c    | 19 +++++++-------
>  security/security.c        | 54 +++++++++++++++++++++++++++++++++++---
>  security/selinux/hooks.c   | 25 ++----------------
>  security/smack/smack.h     |  5 ++++
>  security/smack/smack_lsm.c | 26 +++++++-----------
>  6 files changed, 78 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 0bef312efd45..167ffbd4d0c0 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -2029,6 +2029,7 @@ struct security_hook_list {
>   */
>  struct lsm_blob_sizes {
>         int     lbs_cred;
> +       int     lbs_file;
>  };
>
>  /*
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index c2566aaa138e..15716b6ff860 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -431,21 +431,21 @@ static int apparmor_file_open(struct file *file)
>
>  static int apparmor_file_alloc_security(struct file *file)
>  {
> -       int error = 0;
> -
> -       /* freed by apparmor_file_free_security */
> +       struct aa_file_ctx *ctx = file_ctx(file);
>         struct aa_label *label = begin_current_label_crit_section();
> -       file->f_security = aa_alloc_file_ctx(label, GFP_KERNEL);
> -       if (!file_ctx(file))
> -               error = -ENOMEM;
> -       end_current_label_crit_section(label);
>
> -       return error;
> +       spin_lock_init(&ctx->lock);
> +       rcu_assign_pointer(ctx->label, aa_get_label(label));
> +       end_current_label_crit_section(label);
> +       return 0;
>  }
>
>  static void apparmor_file_free_security(struct file *file)
>  {
> -       aa_free_file_ctx(file_ctx(file));
> +       struct aa_file_ctx *ctx = file_ctx(file);
> +
> +       if (ctx)
> +               aa_put_label(rcu_access_pointer(ctx->label));
>  }
>
>  static int common_file_perm(const char *op, struct file *file, u32 mask)
> @@ -1131,6 +1131,7 @@ static void apparmor_sock_graft(struct sock *sk, struct socket *parent)
>   */
>  struct lsm_blob_sizes apparmor_blob_sizes = {
>         .lbs_cred = sizeof(struct aa_task_ctx *),
> +       .lbs_file = sizeof(struct aa_file_ctx),
>  };
>
>  static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
> diff --git a/security/security.c b/security/security.c
> index ff7df14f6db1..5430cae73cf6 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -40,6 +40,8 @@
>  struct security_hook_heads security_hook_heads __lsm_ro_after_init;
>  static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
>
> +static struct kmem_cache *lsm_file_cache;
> +
>  char *lsm_names;
>  static struct lsm_blob_sizes blob_sizes;
>
> @@ -92,6 +94,13 @@ int __init security_init(void)
>          */
>         do_security_initcalls();
>
> +       /*
> +        * Create any kmem_caches needed for blobs
> +        */
> +       if (blob_sizes.lbs_file)
> +               lsm_file_cache = kmem_cache_create("lsm_file_cache",
> +                                                  blob_sizes.lbs_file, 0,
> +                                                  SLAB_PANIC, NULL);
>         /*
>          * The second call to a module specific init function
>          * adds hooks to the hook lists and does any other early
> @@ -101,6 +110,7 @@ int __init security_init(void)
>
>  #ifdef CONFIG_SECURITY_LSM_DEBUG
>         pr_info("LSM: cred blob size       = %d\n", blob_sizes.lbs_cred);
> +       pr_info("LSM: file blob size       = %d\n", blob_sizes.lbs_file);
>  #endif
>
>         return 0;
> @@ -277,6 +287,28 @@ static void __init lsm_set_size(int *need, int *lbs)
>  void __init security_add_blobs(struct lsm_blob_sizes *needed)
>  {
>         lsm_set_size(&needed->lbs_cred, &blob_sizes.lbs_cred);
> +       lsm_set_size(&needed->lbs_file, &blob_sizes.lbs_file);
> +}
> +
> +/**
> + * lsm_file_alloc - allocate a composite file blob
> + * @file: the file that needs a blob
> + *
> + * Allocate the file blob for all the modules
> + *
> + * Returns 0, or -ENOMEM if memory can't be allocated.
> + */
> +int lsm_file_alloc(struct file *file)
> +{
> +       if (!lsm_file_cache) {
> +               file->f_security = NULL;
> +               return 0;
> +       }
> +
> +       file->f_security = kmem_cache_zalloc(lsm_file_cache, GFP_KERNEL);
> +       if (file->f_security == NULL)
> +               return -ENOMEM;
> +       return 0;
>  }
>
>  /*
> @@ -962,12 +994,28 @@ int security_file_permission(struct file *file, int mask)
>
>  int security_file_alloc(struct file *file)
>  {
> -       return call_int_hook(file_alloc_security, 0, file);
> +       int rc = lsm_file_alloc(file);
> +
> +       if (rc)
> +               return rc;
> +       rc = call_int_hook(file_alloc_security, 0, file);
> +       if (unlikely(rc))
> +               security_file_free(file);
> +       return rc;
>  }
>
>  void security_file_free(struct file *file)
>  {
> +       void *blob;
> +
> +       if (!lsm_file_cache)
> +               return;

Should this be WARN_ON?

> +
>         call_void_hook(file_free_security, file);
> +
> +       blob = file->f_security;
> +       file->f_security = NULL;
> +       kmem_cache_free(lsm_file_cache, blob);
>  }
>
>  int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> @@ -1085,7 +1133,7 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
>                 return rc;
>
>         rc = call_int_hook(cred_alloc_blank, 0, cred, gfp);
> -       if (rc)
> +       if (unlikely(rc))
>                 security_cred_free(cred);
>         return rc;
>  }
> @@ -1106,7 +1154,7 @@ int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp)
>                 return rc;
>
>         rc = call_int_hook(cred_prepare, 0, new, old, gfp);
> -       if (rc)
> +       if (unlikely(rc))
>                 security_cred_free(new);
>         return rc;
>  }
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 94b3123c237b..3468b4592036 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -149,7 +149,6 @@ static int __init checkreqprot_setup(char *str)
>  __setup("checkreqprot=", checkreqprot_setup);
>
>  static struct kmem_cache *sel_inode_cache;
> -static struct kmem_cache *file_security_cache;
>
>  /**
>   * selinux_secmark_enabled - Check to see if SECMARK is currently enabled
> @@ -381,27 +380,15 @@ static void inode_free_security(struct inode *inode)
>
>  static int file_alloc_security(struct file *file)
>  {
> -       struct file_security_struct *fsec;
> +       struct file_security_struct *fsec = selinux_file(file);
>         u32 sid = current_sid();
>
> -       fsec = kmem_cache_zalloc(file_security_cache, GFP_KERNEL);
> -       if (!fsec)
> -               return -ENOMEM;
> -
>         fsec->sid = sid;
>         fsec->fown_sid = sid;
> -       file->f_security = fsec;
>
>         return 0;
>  }
>
> -static void file_free_security(struct file *file)
> -{
> -       struct file_security_struct *fsec = selinux_file(file);
> -       file->f_security = NULL;
> -       kmem_cache_free(file_security_cache, fsec);
> -}
> -
>  static int superblock_alloc_security(struct super_block *sb)
>  {
>         struct superblock_security_struct *sbsec;
> @@ -3558,11 +3545,6 @@ static int selinux_file_alloc_security(struct file *file)
>         return file_alloc_security(file);
>  }
>
> -static void selinux_file_free_security(struct file *file)
> -{
> -       file_free_security(file);
> -}
> -
>  /*
>   * Check whether a task has the ioctl permission and cmd
>   * operation to an inode.
> @@ -6857,6 +6839,7 @@ static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
>
>  struct lsm_blob_sizes selinux_blob_sizes = {
>         .lbs_cred = sizeof(struct task_security_struct),
> +       .lbs_file = sizeof(struct file_security_struct),
>  };
>
>  static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> @@ -6927,7 +6910,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>
>         LSM_HOOK_INIT(file_permission, selinux_file_permission),
>         LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),
> -       LSM_HOOK_INIT(file_free_security, selinux_file_free_security),
>         LSM_HOOK_INIT(file_ioctl, selinux_file_ioctl),
>         LSM_HOOK_INIT(mmap_file, selinux_mmap_file),
>         LSM_HOOK_INIT(mmap_addr, selinux_mmap_addr),
> @@ -7130,9 +7112,6 @@ static __init int selinux_init(void)
>         sel_inode_cache = kmem_cache_create("selinux_inode_security",
>                                             sizeof(struct inode_security_struct),
>                                             0, SLAB_PANIC, NULL);
> -       file_security_cache = kmem_cache_create("selinux_file_security",
> -                                           sizeof(struct file_security_struct),
> -                                           0, SLAB_PANIC, NULL);
>         avc_init();
>
>         avtab_cache_init();
> diff --git a/security/smack/smack.h b/security/smack/smack.h
> index 0c6dce446825..043525a52e94 100644
> --- a/security/smack/smack.h
> +++ b/security/smack/smack.h
> @@ -362,6 +362,11 @@ static inline struct task_smack *smack_cred(const struct cred *cred)
>         return cred->security;
>  }
>
> +static inline struct smack_known **smack_file(const struct file *file)
> +{
> +       return file->f_security;
> +}
> +
>  /*
>   * Is the directory transmuting?
>   */
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index a06ea8aa89c4..d1430341798f 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -1571,24 +1571,12 @@ static void smack_inode_getsecid(struct inode *inode, u32 *secid)
>   */
>  static int smack_file_alloc_security(struct file *file)
>  {
> -       struct smack_known *skp = smk_of_current();
> +       struct smack_known **blob = smack_file(file);
>
> -       file->f_security = skp;
> +       *blob = smk_of_current();
>         return 0;
>  }
>
> -/**
> - * smack_file_free_security - clear a file security blob
> - * @file: the object
> - *
> - * The security blob for a file is a pointer to the master
> - * label list, so no memory is freed.
> - */
> -static void smack_file_free_security(struct file *file)
> -{
> -       file->f_security = NULL;
> -}
> -
>  /**
>   * smack_file_ioctl - Smack check on ioctls
>   * @file: the object
> @@ -1813,7 +1801,9 @@ static int smack_mmap_file(struct file *file,
>   */
>  static void smack_file_set_fowner(struct file *file)
>  {
> -       file->f_security = smk_of_current();
> +       struct smack_known **blob = smack_file(file);
> +
> +       *blob = smk_of_current();
>  }

Is this supposed to be part of a separate patch to prepare smack for
the infrastructure change?

Otherwise, seems good.

-Kees

>
>  /**
> @@ -1830,6 +1820,7 @@ static void smack_file_set_fowner(struct file *file)
>  static int smack_file_send_sigiotask(struct task_struct *tsk,
>                                      struct fown_struct *fown, int signum)
>  {
> +       struct smack_known **blob;
>         struct smack_known *skp;
>         struct smack_known *tkp = smk_of_task(smack_cred(tsk->cred));
>         struct file *file;
> @@ -1842,7 +1833,8 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
>         file = container_of(fown, struct file, f_owner);
>
>         /* we don't log here as rc can be overriden */
> -       skp = file->f_security;
> +       blob = smack_file(file);
> +       skp = *blob;
>         rc = smk_access(skp, tkp, MAY_DELIVER, NULL);
>         rc = smk_bu_note("sigiotask", skp, tkp, MAY_DELIVER, rc);
>         if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
> @@ -4626,6 +4618,7 @@ static int smack_dentry_create_files_as(struct dentry *dentry, int mode,
>
>  struct lsm_blob_sizes smack_blob_sizes = {
>         .lbs_cred = sizeof(struct task_smack),
> +       .lbs_file = sizeof(struct smack_known *),
>  };
>
>  static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
> @@ -4663,7 +4656,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
>         LSM_HOOK_INIT(inode_getsecid, smack_inode_getsecid),
>
>         LSM_HOOK_INIT(file_alloc_security, smack_file_alloc_security),
> -       LSM_HOOK_INIT(file_free_security, smack_file_free_security),
>         LSM_HOOK_INIT(file_ioctl, smack_file_ioctl),
>         LSM_HOOK_INIT(file_lock, smack_file_lock),
>         LSM_HOOK_INIT(file_fcntl, smack_file_fcntl),
> --
> 2.17.1
>
>
diff mbox series

Patch

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 0bef312efd45..167ffbd4d0c0 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2029,6 +2029,7 @@  struct security_hook_list {
  */
 struct lsm_blob_sizes {
 	int	lbs_cred;
+	int	lbs_file;
 };
 
 /*
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index c2566aaa138e..15716b6ff860 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -431,21 +431,21 @@  static int apparmor_file_open(struct file *file)
 
 static int apparmor_file_alloc_security(struct file *file)
 {
-	int error = 0;
-
-	/* freed by apparmor_file_free_security */
+	struct aa_file_ctx *ctx = file_ctx(file);
 	struct aa_label *label = begin_current_label_crit_section();
-	file->f_security = aa_alloc_file_ctx(label, GFP_KERNEL);
-	if (!file_ctx(file))
-		error = -ENOMEM;
-	end_current_label_crit_section(label);
 
-	return error;
+	spin_lock_init(&ctx->lock);
+	rcu_assign_pointer(ctx->label, aa_get_label(label));
+	end_current_label_crit_section(label);
+	return 0;
 }
 
 static void apparmor_file_free_security(struct file *file)
 {
-	aa_free_file_ctx(file_ctx(file));
+	struct aa_file_ctx *ctx = file_ctx(file);
+
+	if (ctx)
+		aa_put_label(rcu_access_pointer(ctx->label));
 }
 
 static int common_file_perm(const char *op, struct file *file, u32 mask)
@@ -1131,6 +1131,7 @@  static void apparmor_sock_graft(struct sock *sk, struct socket *parent)
  */
 struct lsm_blob_sizes apparmor_blob_sizes = {
 	.lbs_cred = sizeof(struct aa_task_ctx *),
+	.lbs_file = sizeof(struct aa_file_ctx),
 };
 
 static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
diff --git a/security/security.c b/security/security.c
index ff7df14f6db1..5430cae73cf6 100644
--- a/security/security.c
+++ b/security/security.c
@@ -40,6 +40,8 @@ 
 struct security_hook_heads security_hook_heads __lsm_ro_after_init;
 static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
 
+static struct kmem_cache *lsm_file_cache;
+
 char *lsm_names;
 static struct lsm_blob_sizes blob_sizes;
 
@@ -92,6 +94,13 @@  int __init security_init(void)
 	 */
 	do_security_initcalls();
 
+	/*
+	 * Create any kmem_caches needed for blobs
+	 */
+	if (blob_sizes.lbs_file)
+		lsm_file_cache = kmem_cache_create("lsm_file_cache",
+						   blob_sizes.lbs_file, 0,
+						   SLAB_PANIC, NULL);
 	/*
 	 * The second call to a module specific init function
 	 * adds hooks to the hook lists and does any other early
@@ -101,6 +110,7 @@  int __init security_init(void)
 
 #ifdef CONFIG_SECURITY_LSM_DEBUG
 	pr_info("LSM: cred blob size       = %d\n", blob_sizes.lbs_cred);
+	pr_info("LSM: file blob size       = %d\n", blob_sizes.lbs_file);
 #endif
 
 	return 0;
@@ -277,6 +287,28 @@  static void __init lsm_set_size(int *need, int *lbs)
 void __init security_add_blobs(struct lsm_blob_sizes *needed)
 {
 	lsm_set_size(&needed->lbs_cred, &blob_sizes.lbs_cred);
+	lsm_set_size(&needed->lbs_file, &blob_sizes.lbs_file);
+}
+
+/**
+ * lsm_file_alloc - allocate a composite file blob
+ * @file: the file that needs a blob
+ *
+ * Allocate the file blob for all the modules
+ *
+ * Returns 0, or -ENOMEM if memory can't be allocated.
+ */
+int lsm_file_alloc(struct file *file)
+{
+	if (!lsm_file_cache) {
+		file->f_security = NULL;
+		return 0;
+	}
+
+	file->f_security = kmem_cache_zalloc(lsm_file_cache, GFP_KERNEL);
+	if (file->f_security == NULL)
+		return -ENOMEM;
+	return 0;
 }
 
 /*
@@ -962,12 +994,28 @@  int security_file_permission(struct file *file, int mask)
 
 int security_file_alloc(struct file *file)
 {
-	return call_int_hook(file_alloc_security, 0, file);
+	int rc = lsm_file_alloc(file);
+
+	if (rc)
+		return rc;
+	rc = call_int_hook(file_alloc_security, 0, file);
+	if (unlikely(rc))
+		security_file_free(file);
+	return rc;
 }
 
 void security_file_free(struct file *file)
 {
+	void *blob;
+
+	if (!lsm_file_cache)
+		return;
+
 	call_void_hook(file_free_security, file);
+
+	blob = file->f_security;
+	file->f_security = NULL;
+	kmem_cache_free(lsm_file_cache, blob);
 }
 
 int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
@@ -1085,7 +1133,7 @@  int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
 		return rc;
 
 	rc = call_int_hook(cred_alloc_blank, 0, cred, gfp);
-	if (rc)
+	if (unlikely(rc))
 		security_cred_free(cred);
 	return rc;
 }
@@ -1106,7 +1154,7 @@  int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp)
 		return rc;
 
 	rc = call_int_hook(cred_prepare, 0, new, old, gfp);
-	if (rc)
+	if (unlikely(rc))
 		security_cred_free(new);
 	return rc;
 }
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 94b3123c237b..3468b4592036 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -149,7 +149,6 @@  static int __init checkreqprot_setup(char *str)
 __setup("checkreqprot=", checkreqprot_setup);
 
 static struct kmem_cache *sel_inode_cache;
-static struct kmem_cache *file_security_cache;
 
 /**
  * selinux_secmark_enabled - Check to see if SECMARK is currently enabled
@@ -381,27 +380,15 @@  static void inode_free_security(struct inode *inode)
 
 static int file_alloc_security(struct file *file)
 {
-	struct file_security_struct *fsec;
+	struct file_security_struct *fsec = selinux_file(file);
 	u32 sid = current_sid();
 
-	fsec = kmem_cache_zalloc(file_security_cache, GFP_KERNEL);
-	if (!fsec)
-		return -ENOMEM;
-
 	fsec->sid = sid;
 	fsec->fown_sid = sid;
-	file->f_security = fsec;
 
 	return 0;
 }
 
-static void file_free_security(struct file *file)
-{
-	struct file_security_struct *fsec = selinux_file(file);
-	file->f_security = NULL;
-	kmem_cache_free(file_security_cache, fsec);
-}
-
 static int superblock_alloc_security(struct super_block *sb)
 {
 	struct superblock_security_struct *sbsec;
@@ -3558,11 +3545,6 @@  static int selinux_file_alloc_security(struct file *file)
 	return file_alloc_security(file);
 }
 
-static void selinux_file_free_security(struct file *file)
-{
-	file_free_security(file);
-}
-
 /*
  * Check whether a task has the ioctl permission and cmd
  * operation to an inode.
@@ -6857,6 +6839,7 @@  static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
 
 struct lsm_blob_sizes selinux_blob_sizes = {
 	.lbs_cred = sizeof(struct task_security_struct),
+	.lbs_file = sizeof(struct file_security_struct),
 };
 
 static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
@@ -6927,7 +6910,6 @@  static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 
 	LSM_HOOK_INIT(file_permission, selinux_file_permission),
 	LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),
-	LSM_HOOK_INIT(file_free_security, selinux_file_free_security),
 	LSM_HOOK_INIT(file_ioctl, selinux_file_ioctl),
 	LSM_HOOK_INIT(mmap_file, selinux_mmap_file),
 	LSM_HOOK_INIT(mmap_addr, selinux_mmap_addr),
@@ -7130,9 +7112,6 @@  static __init int selinux_init(void)
 	sel_inode_cache = kmem_cache_create("selinux_inode_security",
 					    sizeof(struct inode_security_struct),
 					    0, SLAB_PANIC, NULL);
-	file_security_cache = kmem_cache_create("selinux_file_security",
-					    sizeof(struct file_security_struct),
-					    0, SLAB_PANIC, NULL);
 	avc_init();
 
 	avtab_cache_init();
diff --git a/security/smack/smack.h b/security/smack/smack.h
index 0c6dce446825..043525a52e94 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -362,6 +362,11 @@  static inline struct task_smack *smack_cred(const struct cred *cred)
 	return cred->security;
 }
 
+static inline struct smack_known **smack_file(const struct file *file)
+{
+	return file->f_security;
+}
+
 /*
  * Is the directory transmuting?
  */
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index a06ea8aa89c4..d1430341798f 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1571,24 +1571,12 @@  static void smack_inode_getsecid(struct inode *inode, u32 *secid)
  */
 static int smack_file_alloc_security(struct file *file)
 {
-	struct smack_known *skp = smk_of_current();
+	struct smack_known **blob = smack_file(file);
 
-	file->f_security = skp;
+	*blob = smk_of_current();
 	return 0;
 }
 
-/**
- * smack_file_free_security - clear a file security blob
- * @file: the object
- *
- * The security blob for a file is a pointer to the master
- * label list, so no memory is freed.
- */
-static void smack_file_free_security(struct file *file)
-{
-	file->f_security = NULL;
-}
-
 /**
  * smack_file_ioctl - Smack check on ioctls
  * @file: the object
@@ -1813,7 +1801,9 @@  static int smack_mmap_file(struct file *file,
  */
 static void smack_file_set_fowner(struct file *file)
 {
-	file->f_security = smk_of_current();
+	struct smack_known **blob = smack_file(file);
+
+	*blob = smk_of_current();
 }
 
 /**
@@ -1830,6 +1820,7 @@  static void smack_file_set_fowner(struct file *file)
 static int smack_file_send_sigiotask(struct task_struct *tsk,
 				     struct fown_struct *fown, int signum)
 {
+	struct smack_known **blob;
 	struct smack_known *skp;
 	struct smack_known *tkp = smk_of_task(smack_cred(tsk->cred));
 	struct file *file;
@@ -1842,7 +1833,8 @@  static int smack_file_send_sigiotask(struct task_struct *tsk,
 	file = container_of(fown, struct file, f_owner);
 
 	/* we don't log here as rc can be overriden */
-	skp = file->f_security;
+	blob = smack_file(file);
+	skp = *blob;
 	rc = smk_access(skp, tkp, MAY_DELIVER, NULL);
 	rc = smk_bu_note("sigiotask", skp, tkp, MAY_DELIVER, rc);
 	if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
@@ -4626,6 +4618,7 @@  static int smack_dentry_create_files_as(struct dentry *dentry, int mode,
 
 struct lsm_blob_sizes smack_blob_sizes = {
 	.lbs_cred = sizeof(struct task_smack),
+	.lbs_file = sizeof(struct smack_known *),
 };
 
 static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
@@ -4663,7 +4656,6 @@  static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(inode_getsecid, smack_inode_getsecid),
 
 	LSM_HOOK_INIT(file_alloc_security, smack_file_alloc_security),
-	LSM_HOOK_INIT(file_free_security, smack_file_free_security),
 	LSM_HOOK_INIT(file_ioctl, smack_file_ioctl),
 	LSM_HOOK_INIT(file_lock, smack_file_lock),
 	LSM_HOOK_INIT(file_fcntl, smack_file_fcntl),